1. Field of the Invention
The present invention relates to a video input apparatus having separated camera unit and image processing unit connected with each other via a cable.
2. Related Background Art
A conventional video input apparatus having separated camera unit and image processing unit, can replace its camera unit depending upon user's needs. Expensive components such as signal processing circuits and frame memories are used in the image processing unit, and the camera unit can be supplied at low cost.
FIG. 9 is a block diagram showing the structure of a conventional video input apparatus of a camera unit separation type. In FIG. 9, reference numeral 100 represents a camera unit, and reference numeral 200 represents an image processing unit. The camera unit 100 and image processing unit 200 are connected by a cable 300 which is detachably connected to a connector 127 of the camera unit 100 and a connector 238 of the image processing unit 200. Reference numeral 400 represents a host terminal which controls the camera unit 100 and image processing unit 200 and fetches a picked-up image.
In the camera unit 100, reference numeral 124 represents a system control unit made of a one-chip microcomputer having a CPU (central processing unit), a ROM (read-only memory), a RAM (random access memory), and functions of, for example, a control board and a communication board. Reference numeral 120 represents a pickup lens, reference numeral 121 represents an image pickup element such as a CCD, reference numeral 123 represents an image pickup element driving circuit such as a TG (timing generator) which controls the accumulation operation, read operation, and reset operation of the image pickup element 121 in response to control signals from the system control unit 124 to thereby change the shutter speed. Reference numeral 122 represents an S/H AGC circuit for a sampling and holding operation to reduce noises of accumulated charges and for a gain adjustment operation of an image pickup signal in response to control signals from the system control unit to thereby change the gain of the image pickup signal 125. The image pickup signal 125 is supplied via the cable 300 to a signal processing circuit 230 of the image processing unit 200. Reference numeral 126 represents a data line which is connected between the system control unit 124 and the connector 127, the data being transferred via the cable 300 to a system control unit 233 of the image processing unit 200.
In the image processing unit 200, reference numeral 233 represents the system control unit made of a one-chip microcomputer having a CPU, a ROM, a RAM, and functions of, for example, a control board and a communication board. The system control unit 233 performs a control of each device of the image processing unit 200, a control of an auto-white balance, a communication to and from the camera unit 100, and a communication to and from the host terminal 400 via a bus I/F circuit 235. The image processing unit 200 can be detachably mounted on an expansion slot of a computer as a PC card or a signal processing board. For this mount, the bus I/F circuit 235 is used.
Reference numeral 230 represents the signal processing unit which converts an analog video signal on the image pickup signal line 236 transferred from the camera unit 100 via the cable 300, into a standardized digital video signal. Reference numeral 231 represents an encoder circuit which converts the standardized digital video signal into a multiplexed composite signal which is output from a video signal output connector 234. Reference numeral 232 represents a memory circuit which stores a digital video signal from the signal processing circuit 230 and host terminal 400 and controls an image memory read/write. The bus I/F circuit 235 is connected to a bus of the host terminal 400. The bus I/F circuit 235 transfers the digital video signal and control data between the host terminal 400 and image processing unit 200, and controls the memory circuit 232 in response to an instruction from the host terminal 400. Reference numeral 237 represents a data/control line which is used for bidirectional data communications between the host terminal 400 and image processing unit 200, and is connected to a control port of the system control unit 233.
With the video input apparatus constructed as above, the operations of the camera unit 100 and image processing unit 200 can be controlled by the host terminal 400 via the bus I/F circuit 235. For example, in order to change a shutter speed, a shutter speed control command is transferred from the host terminal 400 via the data line 237 of the bus I/F circuit 235 to the system control unit 233 of the image processing unit 200. The system control unit 233 analyzes the received command, and if it is a shutter speed control command, this command is supplied via the data line 126 of the cable 300 to the system control unit 124 of the camera unit 100. Upon reception of this command, the camera unit 100 controls the image pickup element driving circuit 123 to change the shutter speed.
The data transfer procedure of the system control units 233 and 124 of the image processing unit 200 and camera unit 100 is illustrated in FIG. 10. Referring to FIG. 10, when the system control unit 124 of the camera unit 100 receives command data from the system control unit 233 of the image processing unit 200 (S1001), it is checked whether there is any error such as a check sum error, and if an error is detected, an abnormal reception notice is supplied to the system control unit 233 of the image processing unit 200 by using an ACK (acknowledge) frame (S1001). Upon reception of the abnormal reception notice, the system control unit 232 of the image processing unit 200 retransmits the command (S1003, S1005). If an error is not detected, a normal reception notice is supplied to the system control unit 233 of the image processing unit 200 by using the ACK frame (S1006). If an error is detected, an abnormal reception notice is supplied to the system control unit 233 of the image processing unit 200 by using an ACK frame (S1002, S1004).
As above, by detecting an error of data transmission and retransmitting a command when an error is detected, the host can control the camera unit 100 reliably.
The conventional apparatus described above is, however, associated with the following problem. In optimizing a video signal of the camera unit 100 with an AF (auto focus) control function and an AE (auto exposure) control function, it is necessary to read the frequency characteristics and luminance data of a subject necessary for optimization, from the signal processing circuit 230 of the image processing unit 200 and to transmit the read data to the camera unit 100 for the feedback control. This data is read from the signal processing circuit 200 synchronously with the V (vertical) sync signal of video synchronization, and is therefore called V sync data. Data transmission interval is short while this V sync data is transmitted from the image processing unit 200 to the camera unit 100. Therefore, if the procedure of error detection and retransmission illustrated in FIG. 10 is used, the timing of data transmission may be lost.